The nonwovens industry is continually seeking ways to conserve energy in its overall operations. One area which is being examined is the use of aqueous crosslinking resin binder emulsions which require thermal curing. Here the desire is to eliminate or minimize the temperature, or energy. required to cure the resin binders after volatilizing the water while maintaining the properties of the nonwoven product, for instance, wet tensile strength, solvent tensile, brightness, absorbency and like properties.
The use of N-methylolacrylamide-containing copolymer binders in the preparation of nonwoven products is well known in the art. See for example U.S. Pat. Nos. 3,380,851; 3,787,232 and 4,449,978. It is also well known in the art to mix a suitable acid curing agent for the N-methylolacrylamide in order to cure the binder by heating to form a cross-linked interpolymer. Known acidic curing agents include mineral acids, e.g. hydrogen chloride, or organic acids, e.g. oxalic acid, or acid salts such as ammonium chloride.
The nonwoven web of fibers is impregnated with the binder emulsion containing an acidic curing agent and then dried and cured. The nonwoven products are suitably dried by passing them through an air oven or the like and then through a curing oven. Typical laboratory conditions to achieve optimal cross-linking are sufficient time and temperature such as drying at 150.degree. to 200.degree. F. (66.degree.-93.degree. C.) for 4 to 6 minutes, following by curing at 300.degree. to 310.degree. F. (149.degree. to 154.degree. C.) for 3 to 5 minutes or more. However, other time-temperature relationships are employed in industry as is well known in the art, shorter times at higher temperatures or longer times at lower temperatures depending on product grade.